1. Field of the Invention
This invention relates to interocclusal appliances worn in the mouth to prevent tooth structure loss resulting from subconscious parafunctional mandibular habits known as bruxism or clenching.
2. Description of the Prior Art
Bruxism has been found to be a major factor in occlusal tooth surface wear, and may be a significant potential risk factor for dental implant failure. Interocclusal appliances, such as mouth guards or nightguards, have been recognized as beneficial to alleviate the adverse effects of bruxism and clenching.
Prior interocclusal appliances include those that are fitted by a dental professional and those that are self-fitted. Professionally fitted interocclusal appliances are molded of relatively hard acrylic resin from casts of the patient's mouth taken from a dental impression. This procedure requires multiple visits to the dental professional's office, and thus is time-consuming and expensive.
Self-fitted interocclusal appliances typically include a thermoplastic channel or trough in the shape of a maxillary arch. A thermoplastic impressionable liner material is carried in the trough. Such thermoplastic impressionable liner material has a softening point lower than that of the trough. The liner is softened by immersing it in hot water. Then, the liner is molded to conform to a user's mount/teeth by inserting the heated liner into the user's mouth, placing it against the maxillary arch. The user's jaw is closed and biting pressure is applied to force the maxillary teeth into the liner. Representative self-fitted interocclusal appliances of this type are shown in U.S. Pat. Nos. 5,566,684; 6,302,110; and 6,820,623; and European Patent Application No. EP 0 359 135 A1.
Problems were encountered with these prior self-fitting nightguards. Home users had some difficulty fitting the appliance to their own teeth. It can be difficult to properly center and align (register) the heated impressionable liner material of the nightguard relative to one's own maxillary arch. If the fit is not proper, the user could experience discomfort on wearing the nightguard and/or the nightguard could prematurely wear out. In addition, in some prior nightguards, the thermoplastic impressionable liner material was used without a backing plate. Upon severe bruxing or clenching, many users would bite through this material, thus wearing out the appliance and losing the benefit of protecting teeth surfaces. In other prior nightguards, the thermoplastic impressionable liner material separated from the trough as a result of shearing forces from a user's severe bruxing or clenching.
U.S. Pat. No. 6,830,051 illustrates an improved self-fitting interocclusal appliance that includes an impression material unitarily molded to a base material, creating a high shear resistance bond between components. In this prior appliance, the lower base has the shape of a maxillary dental arch. An impression preform of a softenable thermoplastic is molded to the lower base. The inner side walls of the appliance may be tapered inwardly to facilitate proper placement of the appliance in the user's mouth over the user's upper teeth. This appliance thus fits over all upper teeth of the maxillary arch.
Many of the prior self fitting interocclusal appliances include thermoplastic material over all upper teeth of the maxillary arch, including molars and front teeth (incisors and eye teeth). Plastic material between the front lip and front teeth can be uncomfortable. Moreover, when such an appliance is worn, no space or gap is left between the top and bottom teeth. For example, a person's natural bite would generally leave a gap between the upper incisors and the lower incisors. The lack of this gap can lead to breathing difficulties for users accustomed to more mouth breathing at night, such as users who have frequent nasal congestion. An appliance that does not cover or does not substantially cover front teeth, particularly the incisors, would be more comfortable. In addition, when circumstances permit, an appliance that permits greater air flow between upper and lower front teeth would be more comfortable.
For some users, the excess material in an appliance extending over the back molars and/or between the back molars and the cheeks is not comfortable. Such users seek an appliance that satisfactorily protects teeth surfaces without covering all teeth of the maxillary arch. Thus, another alternative appliance with such characteristic would be more comfortable for these users.